Anti-estrogens are the class of drugs which is usually takenduring anabolic steroids cycles. Extremely high concentration of anabolicsteroids hormones in the body, especially testosterone, leads to the fact thatthe excess of testosterone does not have time to completely metabolize whenpassing the physiological pathway. In this case, part of the anabolic steroidhormones passes through the bypass path of metabolism - aromatization, in whichtestosterone is converted into estrogen by the enzyme aromatase. This leads todevelopment of gynecomastia, edema, fat deposition by female type etc. Anti-estrogens, especially Aromatase inhibitors are usedduring steroid cycles to prevent gynecomastia, increase the level of anabolichormones in the blood, prevent hypertension, reduce estrogenic suppression ofthe axis of the hypothalamus-pituitary-testicles. Also by eliminating thenegative effect of estrogens the drugs increase lean muscles, but also can causesome side effects such as braking muscle growth, joint pain, decrease bone strength,increase cholesterol and depression.